1. Field of the Invention
The present invention relates to an imaging apparatus including a strobe device, a strobe device, and a charging-control method for the strobe device. More particularly, the present invention relates to an imaging apparatus including a strobe device having a charging circuit of a separately excited oscillation type, a strobe device, and a charging-control method.
2. Description of the Related Art
In recent years, there have been various types of strobe-charging circuits used for strobe devices or the like. Charging circuits that have been used often lately are of a separately excited oscillation type, and more specifically, of a flyback transformer type. FIG. 9 is a diagram of a configuration example of a strobe-charging circuit of the flyback transformer type.
The strobe-charging circuit shown in FIG. 9, which is a circuit that charges a main capacitor C1 for supplying power to a strobe-light-flashing unit, includes a direct-current power supply 51, a fuse element 52, a step-up transformer 53, a switching element Q1, a feedback capacitor C2, a rectifier diode D1, and the main capacitor C1. The strobe-charging circuit also includes a charging-control unit 61, an oscillation-control unit 62, and a full-charge-detection unit 63, which have functions of controlling the strobe-charging circuit.
The step-up transformer 53 is a flyback transformer that steps up a flyback pulse, which is generated in a primary coil, and that outputs another flyback pulse to a secondary coil. The primary coil is connected in series with the direct-current power supply 51, the fuse element 52, and the switching element Q1. The feedback capacitor C2 is provided between the fuse element 52 and the step-up transformer 53 so as to be connected in parallel to the direct-current power supply 51. A switching group is configured to have the feedback capacitor C2, the primary coil of the step-up transformer 53, and the switching element Q1.
The switching element Q1 is turned on/off on the basis of a switching-control signal from the oscillation-control unit 62. When the switching element Q1 is set to be in a conducting state, a current flows thorough the primary coil of the step-up transformer 53. Then, when the switching element Q1 is set to be in an interrupting state, a counter-electromotive force is generated in the secondary coil of the step-up transformer 53. Accordingly, by continuously turning on/off the switching element Q1, a flyback pulse is generated in the secondarily coil of the step-up transformer 53.
The rectifier diode D1 rectifies the flyback pulse that is generated in the secondary coil of the step-up transformer 53, and supplies a rectified flyback pulse to the main capacitor C1. The main capacitor C1 is charged using the flyback pulse supplied thereto. A charging voltage of the main capacitor C1 is supplied through a power-supply terminal 54 to the strobe-light-flashing unit (not shown in FIG. 9) serving as a load.
The charging-control unit 61 is a processing unit that performs overall control on the strobe-charging circuit. After a strobe-light-flashing operation is performed in the strobe-light-flashing unit, the charging-control unit 61 provides an instruction for starting an oscillation of the switching-control signal to the oscillation-control unit 62. When the full-charge-detection unit 63 detects a fully charged state of the main capacitor C1, the charging-control unit 61 stops an oscillation operation of the oscillation-control unit 62. The full-charge-detection unit 63 determines whether or not the main capacitor C1 is in the fully charged state, for example, by detecting a voltage across the terminals of the main capacitor C1.
In an example of such a strobe-charging circuit of a separately excited oscillation type, when a charging voltage of a main capacitor reaches a predetermined voltage higher than a light-flashing voltage, an oscillation-control unit is reset to stop a charging operation (for example, see paragraphs [0037] to [0042] and FIG. 1 in Japanese Unexamined Patent Application Publication No. 2000-275706). In another example, a value of a current flowing through a primary coil of an oscillation transformer, or a value of a voltage generated by the current, is compared with a value of a normal-operating current, or voltage, and a charging voltage of a main capacitor is compared with a value of a charging voltage in a normal operation, respectively. Then, as an occasional result of the comparison, a series circuit in which a power supply and a fuse are connected in series is shorted to ground by a switching element, thereby blowing the fuse, so that a supply of power is interrupted in the circuit (for example, see paragraphs [0008] to [0012] and FIG. 4 in Japanese Unexamined Patent Application Publication No. 2007-48702).